In the U.S., morbidity associated with human rhinovirus (RV) infection represents a major health problem. In asthmatics, up to 80% of asthma exacerbations are associated with upper respiratory infections. Despite evidence that environmental oxidant pollutants, such as ozone, may increase the severity of viral disease, the mechanisms underlying such an effect have not been identified. This study will test the hypothesis that exposure of allergic asthmatic subjects to ambient levels of ozone directly enhances viral disease by increasing infectivity and intensifying virus-induced inflammation.